The invention relates to a powered vehicle.
German Offenlegungsschrift No. 40 11 850 discloses a motor vehicle which employs so-called xe2x80x9celectronic clutch managementxe2x80x9d (ECM) system. The motor vehicle has a combustion engine, a multispeed manual transmission, an automatic clutch for coupling the engine to the transmission and a control unit for the clutch.
Under certain circumstances it is unsafe for the operator of such a motor vehicle to exit such a vehicle. For instance, if the vehicle is stationary and in gear with the engine idling, as may be the case when standing in front of a garage (the clutch is then in a standby position because the gas pedal is not depressed), a fault in the release system, e.g., a pressure drop in the hydraulic unit, could cause the clutch to close, that is, to engage the transmission. However, the driver is not warned to remain in the vehicle.
The sensitivity with which the moment exerted by the engine is transferred to the drive gears, e.g., while shifting, is also not entirely satisfactory. This has an adverse effect on the comfort of the vehicle. Moreover, it is difficult to set the vehicle in motion on icy roads. In addition, the vehicle is relatively expensive.
Furthermore, neither the sensitivity nor the speed of the control system is totally adequate and faults in the system are not readily detectable by the operator or by a repair shop. The electronic hardware is relatively complex and cannot be used universally. Additionally, the number of masters and slaves is rather large, and fairly extensive vehicle modifications are required in order to use the known version of the ECM system.
It is an object of the invention to improve the safety of an ECM-equipped vehicle.
Another object of the invention is to provide warning to an operator of an ECM-equipped vehicle when a particular combination of conditions makes it unsafe to exit the vehicle.
An additional object of the invention is to increase the comfort of an ECM-equipped vehicle.
A further object of the invention is to increase the sensitivity with which the moment generated by the engine of an ECM-equipped vehicle is transferred to the drive gears.
It is also an object of the invention to provide an ECM-equipped vehicle which can be set into motion relatively easily, even on icy roads.
Still another object of the invention is to provide an ECM system which can be manufactured relatively economically.
An additional object of the invention is to increase the sensitivity of an ECM system.
A further object of the invention is to increase the speed of an ECM system.
A concomitant object of the invention is to provide an ECM system capable of advising a vehicle operator or repair shop of faults in the system.
It is also an object of the invention to provide an ECM system which can store fault indications for subsequent recall.
Yet another object of the invention is to simplify the electronic hardware for an ECM system.
An additional object of the invention is to provide electronic hardware which is or can be used in an ECM system and has relatively widespread applicability.
A further object of the invention is to provide an ECM system which allows the number of masters and slaves to be reduced.
A concomitant object of the invention is to provide an ECM system which requires relatively few vehicle modifications.
It is an additional object of the invention to provide a method which enables a vehicle to be operated with increased safety.
The preceding objects, as well as others which will become apparent as the description proceeds, are achieved by the invention.
One aspect of the invention resides in a powered vehicle comprising an engine, e.g., an internal combustion engine, and means for regulating the speed of the engine by an operator of the vehicle. The regulating means has a plurality of positions including a rest position in which the engine is at idling speed and an operative position in which the engine is above idling speed. The vehicle further comprises a manual transmission, a clutch for coupling the engine to the transmission, and means for automatically controlling the clutch. The clutch is movable in a first direction to engage the transmission and in a second direction to disengage from the transmission, and the clutch has a predetermined position in which the clutch engages the transmission with a predetermined force such that the vehicle begins to creep. The controlling means includes means for moving the clutch to the predetermined position under predetermined conditions in which the vehicle is in gear and at a standstill or almost so, the engine is running and the regulating means is in the rest position. The regulating means can comprise a gas pedal, for example.
Another aspect of the invention resides in a method of operating a vehicle having an engine, a manual transmission and a clutch for coupling the engine to the transmission. The method comprises the steps of idling the engine while the vehicle is in gear and at a standstill or almost so, and automatically engaging the clutch with the transmission in such a manner that the vehicle begins to creep.
According to the invention, after the vehicle is stopped by means of the foot brake or hand brake, the vehicle begins to creep if the engine is running and the vehicle is in gear. The operator of the vehicle thus does not even think of leaving the vehicle so that safety is increased. Creeping of the vehicle also provides greater comfort and better handling characteristics during parking, shifting and starting off on icy roads because greater sensitivity is achieved.
It is of advantage for the clutch to be moved in the direction of opening, i.e., in the direction of disengagement from the transmission, if the foot brake and/or hand brake is applied during creeping. The moment or torque being transferred is thereby reduced. The clutch may be steadily or abruptly urged in the direction of disengagement, e.g., to a standby, waiting or offset position which the clutch assumes preparatory to engaging the transmission.
When the vehicle is stationary or practically stationary and is placed in gear with the brake applied and the gas pedal at rest, the clutch may be held in a position, i.e., the standby position, which is set back from the predetermined position of the clutch during creeping.
If neither the brake nor the gas pedal is applied during creeping so that the vehicle is in an idling mode, the clutch can be continuously urged in the direction of closing, that is, in the direction of engagement with the transmission. This prevents the clutch from overheating by the relatively great slippage which accompanies steady creeping. The speed of the vehicle thus increases continuously.
The standby position may be obtained by determining the so-called initial engagement point of the clutch at which the clutch just begins to transfer moment and automatically adding a small setback or offset to this point in the direction of disengagement. The resulting value can be stored in electronic hardware, e.g., an electronic memory or a computer, and recalled from there as necessary or sent to an appropriate receiver.
When the vehicle is stationary or practically stationary with the engine running and both the gas pedal and brake inoperative, the clutch may be moved out of a position of disengagement in response to shifting of the vehicle into gear. Advantageously, the clutch is continuously urged in the direction of engagement so that the vehicle begins to creep and slippage is steadily reduced. Due to the reduction in slippage, the speed at which the vehicle creeps increases constantly. Urging of the clutch in the direction of engagement can be interrupted when the brake is applied and the clutch may be shifted in the direction of disengagement, e.g., to the standby position.
The clutch may automatically move into engagement with the transmission after the engine is shut off. It is of particular advantage for the clutch to engage the transmission when the vehicle is in gear to thus reliably lock the transmission. If the vehicle is in gear when the engine is shut off, movement of the clutch into engagement with the transmission preferably occurs with a short delay following engine shutdown because the engine can continue running after the ignition is shut off.
After starting of the engine, which favorably can take place only in neutral, the clutch may be moved into a position downstream of the initial engagement point as considered in the direction of disengagement. By way of example, this position can be the fully open or disengaged condition or position of the clutch. Upon shifting of the vehicle into a starting gear, i.e., low gear, the clutch is moved into the standby position. Such changes in the condition of the clutch can occur, for instance, in response to detection of a particular gear by a gear detection unit.
As mentioned previously, if the vehicle is in gear and the gas pedal is inactive, the clutch can move out of a disengaged position, such as the standby position, in the direction of engagement. The clutch may be steadily urged in the direction of engagement so that the vehicle begins to creep. Displacement of the clutch in the direction of engagement is preferably regulated, and movement of the clutch from the standby position to the initial engagement position and/or from the initial engagement position to a more firmly engaged or fully engaged position may take place in accordance with a moment-time function or in dependence upon the slippage between the engine and the transmission. The larger of the slippage and the moment-time function controls the displacement of the clutch.
Movement of the clutch in the direction of engagement, e.g., from the standby position to the initial engagement position and/or from the initial engagement position to the fully engaged position, can occur without direct determination of the speed of the transmission. Thus, instead of measuring the transmission input speed directly, a value representing this input speed is derived from the speed of the vehicle. For example, a signal indicative of the speed of the vehicle can be obtained from a control unit such as a digital engine electronics unit. The speed achieved downstream of the clutch along the path of force transfer from the engine to the transmission, i.e., the transmission input speed, can be calculated by taking into account the gear in which the vehicle is operating and the corresponding gear ratio. The electronic hardware can calculate the transmission input speed very simply inasmuch as a signal representative of vehicle speed is always available and the gear ratio which can be stored in the electronic unit allows a backward computation to be performed. The gear in which the vehicle is operating is obtained from the so-called gear detection unit. With such an arrangement, a sensor for determining the transmission input speed can be eliminated and no changes need be made in the manual transmission when using an ECM system according to the invention.
The initial engagement point corresponds, at least approximately, to the position of the clutch when the vehicle begins to creep. Advantageously, the starting position of the clutch for the engagement procedure, which takes place after engine start-up, is the initial engagement point corrected by the offset.
The displacement of the clutch can be measured by an element of the release system which is remote from the clutch operating means, such as the release bearing. In a fluid-operated release system, e.g., a hydraulic system, the displacement can be directly and indirectly measured by the master cylinder. To this end, the rod of the hydraulic cylinder can activate a lever which is pivotally connected to a rotary potentiometer. This type of measuring system is of particular advantage because no changes need be made to the transmission jacket or bell. However, a volume change of the hydraulic fluid due to temperature variations is unavoidable. Hence, the relationship between the actual clutch position at the slave cylinder and the clutch position as measured by the master cylinder may be in error, at least until volume compensation takes place via an equalizing bore which connects the working fluid with a supply vessel for hydraulic fluid. The hydraulic clutch operating system can be connected to the brake fluid circuit.
To compensate for, or rule out, such errors, the initial engagement point may be determined by more than one method.
One method of determining the initial engagement point takes place with the vehicle in neutral and at a standstill or almost so. The initial engagement point obtained under these conditions may be referred to as a stationary initial engagement point, and the determination of this engagement point is advantageously performed periodically.
A second stationary initial engagement point can be established in addition to, or instead of, the first such engagement point described above. The second stationary initial engagement point is determined with the foot brake applied and the vehicle in gear at a standstill or almost so. It is again of advantage for the determination of the second stationary initial engagement point to be carried out periodically.
The stationary initial engagement points, which may be determined by means of a potentiometer, can be sent to a memory.
In accordance with the invention, another method of determining the initial engagement point is carried out while the vehicle is coasting and/or while the engine is under load. The initial engagement point established during coasting is referred to as the coasting initial engagement point, whereas the initial engagement point determined with the engine under load is referred to as the loaded initial engagement point.
The coasting initial engagement point can be determined with the gas pedal inoperative and the clutch in a position downstream of the standby position in the direction of engagement. The minimum speed of the engine is established, and this can be accomplished by detecting the increase in engine speed which follows a drop in speed, that is, by detecting the first positive gradient. This is a condition where the moment which can actually be transferred by the clutch equals the moment generated by the engine while coasting. The minimum engine speed is related to a specific coasting or braking moment of the engine by means of a characteristic engine curve stored in the electronic hardware. The coasting or braking moment, in turn, is related to the spacing from the potential, i.e., the nearest initial engagement point, via a characteristic clutch curve likewise stored in the electronic hardware.
By way of example, the loaded initial engagement point can be established by integrating the difference in speed between the engine and the transmission, i.e., the slippage, over time. When the resulting integral is a first predetermined amount less than a first value, the initial engagement point is corrected in the direction of engagement. On the other hand, when the integral exceeds a second value by a second predetermined amount, the initial engagement point is corrected in the direction of disengagement.
Similarly to the stationary initial engagement point, the coasting and loaded initial engagement points can be sent to a memory. Advantageously, the stationary initial engagements points are stored in a volatile memory while the coasting and loaded initial engagement points are stored in a nonvolatile memory.
Whether the coasting initial engagement point or loaded initial engagement point is determined depends upon the particular application. In many cases, however, it is of advantage to establish and store both of these engagement points.
A volatile central memory can be provided for the established standby positions. This memory could also serve to store an initial engagement point which, as described above, is adjusted by a predetermined value. The central memory can be connected with the volatile memory for the stationary initial engagement points and the nonvolatile memory for the coasting and loaded initial engagement points. These initial engagement points can then be transferred to the central memory. The values in the volatile memory for the stationary initial engagement points can be recalled by the central memory after each determination, e.g., in response to arrival of the clutch at the standby position.
The stored coasting and/or loaded initial engagement points can be transferred to the central memory in response to complete closing of the clutch, that is, in response to full engagement of the clutch and the transmission. If, for example, the vehicle is to operate in a slippage mode, the coasting and/or loaded initial engagement points may be recalled by the central memory when the clutch is in almost, but not quite, full engagement with the transmission. Transfer of information regarding the coasting and/or loaded initial engagement points to the central memory can also take place in response to arrival placing of the clutch at a position into a condition of engagement with the transmission such that the moment transmittable by the clutch exceeds the instantaneous moment of the engine.
Alternatively, information pertaining to the coasting and/or loaded initial engagement points can be recalled by the central memory when the clutch opens completely or almost so, that is, when the clutch is at or near its condition of maximum distance from the transmission disengagement. In many cases, it can be of advantage for transfer of the coasting and/or loaded initial engagement points to occur in response to placing of the clutch at into the standby condition.
It is also possible for the coasting and/or loaded initial engagement points to be transferred to the central memory when the master cylinder assumes a condition in which volume compensation takes place, via the equalizing bore, with the hydraulic fluid supply vessel. This is generally the case when the clutch is engaged.
The central memory holds the coasting and loaded initial engagement points in readiness for the control unit or passes them on to such unit.
The latest stationary initial engagement point to be determined can be sent to the central volatile memory just before the clutch becomes engaged. This latest point is erased once the clutch has been engaged for a short period, e.g., one second, and volume compensation has occurred in the hydraulic clutch release system via the equalizing bore. On the other hand, the coasting and/or loaded initial engagement points stored in the nonvolatile or adaptive memory may be transferred to the central memory at this time.
When the engine is shut off, the central memory and the memory for the stationary initial engagement points are erased. In contrast, the coasting and/or loaded initial engagement points present in the nonvolatile memory remain in storage and, when the engine is next started, are fed into the central memory and used to control displacement of the clutch to the position of initial engagement.
Movement of the clutch from a fully, or almost fully, open position to the standby position can be regulated by means of an e-function. During acceleration, movement of the clutch out of the standby position in the direction of engagement can occur in dependence upon a reference speed which, in turn, is a function of the position of the load lever, that is, the gas pedal or accelerator.
When shifting, the displacement of the clutch from the standby position into renewed engagement with the transmission can take place in dependence upon a reference slippage. By means of a time curve or ramp, the reference slippage can be adjusted with respect to a desired final slippage on the basis of the actual slippage at the time of initial engagement. If, for instance, travel is not to occur with a slipping clutch in order to insulate against vibrations, the desired final slippage can be zero.
The moment applied to the clutch may equal or exceed the moment generated by the engine. The engine moment can be determined from the engine speed and the position of the load lever.
The reference moment of the clutch, as determined by the control unit or control algorithm activated under particular operating conditions (creeping and/or acceleration and/or re-engagement), may be converted into a reference displacement via the characteristic curve of the clutch. The reference displacement can be compared with the actual position of the clutch in a displacement control circuit to generate a comparative value. The required reference flow for valve regulation can be determined from this comparative value in a PID controller.